Aortic wall mechanics in the Marfan syndrome assessed by transesophageal tissue Doppler echocardiography

The predictive capability of aortic stiffness index for aortic dissection among dilated ascending aortas

OBJECTIVE

We created a finite element model to predict the probability of dissection based on imaging-derived aortic stiffness and investigated the link between stiffness and wall tensile stress using our model.

METHODS

Transthoracic echocardiogram measurements were used to calculate aortic diameter change over the cardiac cycle. Aortic stiffness index was subsequently calculated based on diameter change and blood pressure. A series of logistic models were developed to predict the binary outcome of aortic dissection using 1 or more series of predictor parameters such as aortic stiffness index or patient characteristics. Finite element analysis was performed on a subset of diameter-matched patients exhibiting patient-specific material properties.

RESULTS

Transthoracic echocardiogram scans of patients with type A aortic dissection (n = 22) exhibited elevated baseline aortic stiffness index when compared with aneurysmal patients' scans with tricuspid aortic valve (n = 83, P < .001) and bicuspid aortic valve (n = 80, P < .001). Aortic stiffness index proved an excellent discriminator for a future dissection event (area under the curve, 0.9337, odds ratio, 2.896). From the parametric finite element study, we found a correlation between peak longitudinal wall tensile stress and stiffness index (ρ = .6268, P < .001, n = 28 pooled).

CONCLUSIONS

Noninvasive transthoracic echocardiogram-derived aortic stiffness measurements may serve as an impactful metric toward predicting aortic dissection or quantifying dissection risk. A correlation between longitudinal stress and stiffness establishes an evidence-based link between a noninvasive stiffness parameter and stress state of the aorta with clinically apparent dissection events.

Endothelial dysfunction in Marfan syndrome mice is restored by resveratrol

Patients with Marfan syndrome (MFS) develop thoracic aortic aneurysms as the aorta presents excessive elastin breaks, fibrosis, and vascular smooth muscle cell (vSMC) death due to mutations in the FBN1 gene. Despite elaborate vSMC to aortic endothelial cell (EC) signaling, the contribution of ECs to the development of aortic pathology remains largely unresolved. The aim of this study is to investigate the EC properties in Fbn1^C1041G/+ MFS mice. Using en face immunofluorescence confocal microscopy, we showed that EC alignment with blood flow was reduced, EC roundness was increased, individual EC surface area was larger, and EC junctional linearity was decreased in aortae of Fbn1^C1041G/+ MFS mice. This modified EC phenotype was most prominent in the ascending aorta and occurred before aortic dilatation. To reverse EC morphology, we performed treatment with resveratrol. This restored EC blood flow alignment, junctional linearity, phospho-eNOS expression, and improved the structural integrity of the internal elastic lamina of Fbn1^C1041G/+ mice. In conclusion, these experiments identify the involvement of ECs and underlying internal elastic lamina in MFS aortic pathology, which could act as potential target for future MFS pharmacotherapies.

Fibrillin-1 Gene Polymorphisms (rs145233125, rs11070646, rs201170905) Are Associated With the Susceptibility and Clinical Prognosis of DeBakey Type III Aortic Dissection in Chinese Han Population

ABSTRACT

We aim to investigate whether genetic variants of the Fibrillin-1 (FBN1) gene were associated with DeBakey type III aortic dissection (AD) and its clinical prognosis in Chinese Han population. Three single-nucleotide polymorphisms (SNPs) (rs145233125, rs11070646, rs201170905) in FBN1 were analyzed in patients with DeBakey type III AD (159) and healthy subjects (216). Gene-environment interactions were evaluated to use generalized multifactor dimensionality reduction. Haplotype analysis of the 3 SNPs in the FBN1 gene was performed by Haploview software. Patients were followed up for average 4 years. G carriers of rs11070646 and rs201170905 in FBN1 have an increased risk of DeBakey type III AD. The interaction of FBN1 and environmental factors facilitated to the increased risk of DeBakey type III AD (cross-validation consistency = 10/10, P = 0.001). One of the most common haplotypes revealed an increased risk of DeBakey type III AD (CGG, P = 0.009). Recessive models of rs145233125 CC genotype ( P < 0.05) and rs201170905 GG genotype ( P < 0.001) were associated with an increased risk of death and recurrent chest pain of DeBakey type III AD. In conclusions, FBN1 gene polymorphisms contribute to DeBakey type III AD susceptibility. The interactions of gene and environment are related with the risk of DeBakey type III AD. C carriers of rs145233125 and G carriers of rs201170905 may be the adverse prognostic indicators of death and recurrent chest pain in DeBakey type III AD.

Patient-Specific Inverse Modeling of In Vivo Cardiovascular Mechanics with Medical Image-Derived Kinematics as Input Data: Concepts, Methods, and Applications

Inverse modeling approaches in cardiovascular medicine are a collection of methodologies that can provide non-invasive patient-specific estimations of tissue properties, mechanical loads, and other mechanics-based risk factors using medical imaging as inputs. Its incorporation into clinical practice has the potential to improve diagnosis and treatment planning with low associated risks and costs. These methods have become available for medical applications mainly due to the continuing development of image-based kinematic techniques, the maturity of the associated theories describing cardiovascular function, and recent progress in computer science, modeling, and simulation engineering. Inverse method applications are multidisciplinary, requiring tailored solutions to the available clinical data, pathology of interest, and available computational resources. Herein, we review biomechanical modeling and simulation principles, methods of solving inverse problems, and techniques for image-based kinematic analysis. In the final section, the major advances in inverse modeling of human cardiovascular mechanics since its early development in the early 2000s are reviewed with emphasis on method-specific descriptions, results, and conclusions. We draw selected studies on healthy and diseased hearts, aortas, and pulmonary arteries achieved through the incorporation of tissue mechanics, hemodynamics, and fluid-structure interaction methods paired with patient-specific data acquired with medical imaging in inverse modeling approaches.

Is physical activity a future therapy for patients with Marfan syndrome?

Introduction

The international recommendations tend to avoid physical activity (PA) for patients with Marfan syndrome (MFS). However, exceptions have recently been made in the most recent recommendations for these patients, suggesting benefits from doing PA at low intensity only. Furthermore, there is no evidence that moderate aerobic or weight training can worsen the disease symptoms and increase mortality of MFS patients. The present review sums up the work carried out in the field of PA and MFS. The review aims to (1) identify the different types of exercise testing and training protocols and (2) discuss the feasibility and potentially beneficial nature of PA as an innovative way to manage MFS patients.

Methods

The scientific literature was reviewed using the following words: Marfan syndrome, training, physical activity, evaluation, weight training, arterial disease, aneurysms, lung damage, aortic dissection, rupture. A total of 345 studies were prospected and 43 studies were included.

Conclusions

A limited number of studies were done in humans, however one demonstrated the feasibility of the management of MFS patients with PA. There were potential beneficial effects of PA on arterial structures, but this review also showed deleterious effects when PA was conducted at high intensities, corresponding to 75–85% of the maximal oxygen uptake. However, these effects have only been reported in animal studies.

Left Ventricular Concentric Geometric Patterns Are Associated With Worse Prognosis Among Patients With Type-A Aortic Dissection

Background

This study compared left ventricular (LV) characteristics between patients with type‐A and type‐B aortic dissection (AD) and evaluated the ability of LV remodeling phenotypes (hypertrophy, concentricity, or geometric patterns) to predict mortality in both AD types.

Methods and Results

We evaluated 236 patients with type A and 120 patients with type B who had echocardiograms within 60 days before or after AD diagnosis (median [25th, 75th percentiles] time difference between echocardiogram and AD diagnosis=1 [0, 6] days) from 3 centers. Patients were stratified according to LV phenotypes, and early (90‐day) and late (1‐year) mortality after AD diagnosis were assessed. In adjusted logistic regression analysis, patients with type A had higher and lower odds of concentric and eccentric hypertrophy (odds ratio [OR], 2.56; 95% CI, 1.50–4.36; P<0.001; and OR, 0.55; 95% CI, 0.31–0.97; P=0.039, respectively) than those with type B. Results of multivariable Cox‐regression analysis showed that LV remodeling phenotypes were not related to mortality in patients with type B. By contrast, LV concentricity was associated with greater early and late mortality (hazard ratio [HR], 2.22; 95% CI, 1.24–3.96; P=0.007 and HR, 2.06; 95% CI, 1.20–3.54; P=0.009, respectively) in type A. In further analysis considering normal LV geometry as reference, LV concentric remodeling and concentric hypertrophy were associated with early mortality (HR, 7.78; 95% CI, 2.35–25.78; P<0.001 and HR, 4.38; 95% CI, 1.47–13.11; P=0.008, respectively), whereas concentric remodeling was associated with late mortality (HR, 5.40; 95% CI, 1.91–15.26; P<0.001) among patients with type A. Assessment of LV geometric patterns and concentricity provided incremental prognostic value in predicting early and late mortality beyond clinical variables in patients with type A based on net reclassification improvement and integrated discrimination improvement.

Conclusions

LV geometric patterns derived from LV concentricity were associated with greater mortality among patients with type A and may be markers of adverse prognosis in this population.

Aortic Regurgitation Is Associated With Ascending Aortic Remodeling in the Nondilated Aorta

OBJECTIVE

The probability of aortic complications in patients with bicuspid aortic valve is higher in association with aortic regurgitation (AR) compared with aortic stenosis (AS) or normally functioning valves. The objective of this study was to determine whether this is related to the specific characteristics of aneurysmatic dilatation that includes AR or whether AR itself has a negative impact on the aortic wall, independent of aneurysmatic dilatation. Approach and Results: Nondilated aortic specimens were harvested intraoperatively from individuals with tricuspid aortic valves and either AS (n=10) or AR (n=16). For controls, nondilated aortas were harvested during autopsies from individuals with tricuspid aortic valves and no evidence of aortic valve disease (n=10). Histological and immunohistochemical analyses revealed that compared with control aortas, overall medial degeneration was more severe in AR-aortas (P=0.005) but not AS-aortas (P=0.23). This pathological remodeling included mucoid extracellular matrix accumulation (P=0.005), elastin loss (P=0.003), elastin fragmentation (P=0.008), and decreased expression of fibrillin (P=0.003) and collagen (P=0.008). Furthermore, eNOS (endothelial nitric oxide synthase) expression was decreased in the intima (P=0.0008) and in vasa vasorum (P=0.004) of AR-aortas but not AS-aortas (all P>0.05). Likewise, subendothelial apoptosis was increased in AR-aortas (P=0.03) but not AS-aortas (P=0.50).

CONCLUSIONS

AR has a negative effect on the nondilated ascending aortic wall. Accordingly, our results support the need for more detailed studies of the aortic wall in relation to aortic valve disease and may ultimately lead to more aggressive clinical monitoring and/or surgical criteria for patients with relevant AR. Graphic Abstract: A graphic abstract is available for this article.

Systolic stretching of the ascending aorta

INTRODUCTION

Longitudinal stretching of the aorta due to systolic heart motion contributes to the stress in the wall of the ascending aorta. The objective of this study was to assess longitudinal systolic stretching of the aorta and its correlation with the diameters of the ascending aorta and the aortic root.

MATERIAL AND METHODS

Aortographies of 122 patients were analyzed. The longitudinal systolic stretching of the aorta caused by the contraction of the heart during systole and the maximum dimensions of the aortic root and ascending aorta were measured in all patients.

RESULTS

The maximum dimension of the aortic root was on average 34.9 ±4.5 mm and the mean diameter of the ascending aorta was 33.9 ±5.4 mm. The systolic aortic stretching negatively correlated with age (r = -0.49, p < 0.001) and the diameter of the tubular ascending aorta (r = -0.44, p < 0.001). There was no significant correlation between the stretching and the dimension of the aortic root (r = -0.11, p = 0.239). There was a statistically significant (p < 0.001) difference in the longitudinal aortic stretching values between patients with a normal aortic valve (10.6 ±3.1 mm) and an aortic valve pathology (8.0 ±3.2 mm in all patients with an aortic valve pathology; 7.5 ±4.3 mm in isolated aortic stenosis, 8.5 ±2.9 mm in the case of isolated insufficiency, 8.2 ±2.8 mm for valves that were both stenotic and insufficient).

CONCLUSIONS

Systolic aortic stretching negatively correlates with the diameter of the tubular ascending aorta and the age of the patients, and does not correlate with the diameter of the aortic root. It is lower in patients with an aortic valve pathology.

Assessing Patient-Specific Mechanical Properties of Aortic Wall and Peri-Aortic Structures From In Vivo DENSE Magnetic Resonance Imaging Using an Inverse Finite Element Method and Elastic Foundation Boundary Conditions

The establishment of in vivo, noninvasive patient-specific, and regionally resolved techniques to quantify aortic properties is key to improving clinical risk assessment and scientific understanding of vascular growth and remodeling. A promising and novel technique to reach this goal is an inverse finite element method (FEM) approach that utilizes magnetic resonance imaging (MRI)-derived displacement fields from displacement encoding with stimulated echoes (DENSE). Previous studies using DENSE MRI suggested that the infrarenal abdominal aorta (IAA) deforms heterogeneously during the cardiac cycle. We hypothesize that this heterogeneity is driven in healthy aortas by regional adventitial tethering and interaction with perivascular tissues, which can be modeled with elastic foundation boundary conditions (EFBCs) using a collection of radially oriented springs with varying stiffness with circumferential distribution. Nine healthy IAAs were modeled using previously acquired patient-specific imaging and displacement fields from steady-state free procession (SSFP) and DENSE MRI, followed by assessment of aortic wall properties and heterogeneous EFBC parameters using inverse FEM. In contrast to traction-free boundary condition, prescription of EFBC reduced the nodal displacement error by 60% and reproduced the DENSE-derived heterogeneous strain distribution. Estimated aortic wall properties were in reasonable agreement with previously reported experimental biaxial testing data. The distribution of normalized EFBC stiffness was consistent among all patients and spatially correlated to standard peri-aortic anatomical features, suggesting that EFBC could be generalized for human adults with normal anatomy. This approach is computationally inexpensive, making it ideal for clinical research and future incorporation into cardiovascular fluid-structure analyses.

Myocardial Function, Heart Failure and Arrhythmia in Marfan Syndrome: A Systematic Literature Review

Marfan syndrome (MFS) is a heritable systemic connective tissue disease with important cardiovascular involvement, including aortic root dilatation and mitral valve prolapse. Life expectancy in patients with MFS is mainly determined by cardiovascular complications, among which aortic dissection or rupture are most dreaded. In recent years, heart failure and ventricular arrhythmia have drawn attention as extra-aortic cardiovascular manifestations and as additional reported causes of death. Imaging studies have provided data supporting a primary myocardial impairment in the absence of valvular disease or cardiovascular surgery, while studies using ambulatory ECG have demonstrated an increased susceptibility to ventricular arrhythmia. In this paper, current literature was reviewed in order to provide insights in characteristics, pathophysiology and evolution of myocardial function, heart failure and ventricular arrhythmia in MFS.

The use of ultrasound to assess aortic biomechanics: Implications for aneurysm and dissection

Arterial stiffening, which occurs when conduit arteries thicken and lose elasticity, has been associated with cardiovascular disease and increased risk for future cardiovascular events. Specifically, aortic stiffening plays a large role in the pathogenesis of vascular diseases, such as aneurysm formation and dissection. Current parameters used to assess risk of aortic rupture include absolute diameter and growth rate. However, these properties lack the reliability required to accurately risk-stratify patients. As with any elastic conduit, it is important to assess the biomechanical properties of the aorta in order to assess cardiovascular risk and prevent disease progression. There are several invasive and noninvasive methods by which stiffness of the large arteries can be assessed. Of particular interest are ultrasound-based methods, such as tissue Doppler imaging and speckle-tracking echocardiography, due to their noninvasive and feasible nature. In this review, we summarize studies demonstrating utility of noninvasive ultrasound imaging methods for measuring aortic biomechanics for the assessment and management of aortic aneurysms.

Unreliable Estimation of Aortic Pulse Wave Velocity Provided by the Mobil-O-Graph Algorithm-Based System in Marfan Syndrome

Background Several devices have been proposed to assess arterial stiffness in clinical daily use over the past few years, by estimating aortic pulse wave velocity (PWV) from a single measurement of brachial oscillometric blood pressure, using patented algorithms. It is uncertain if these systems are able to provide additional elements, beyond the contribution carried by age and blood pressure levels, in the definition of early vascular damage expressed by the stiffening of the arterial wall. Methods and Results The aim of our study was to compare the estimated algorithm-based PWV values, provided by the Mobil-O-Graph system, with the standard noninvasive assessment of aortic PWV in patients with Marfan syndrome (ie, in subjects characterized by premature aortic stiffening and low blood pressure values). Aortic stiffness was simultaneously evaluated by carotid-femoral PWV with a validated arterial tonometer and estimated with an arm cuff-based ambulatory blood pressure monitoring Mobil-O-Graph device on 103 patients with Marfan syndrome (50 men; mean± SD age, 38±15 years). Aortic PWV, estimated by the Mobil-O-Graph, was significantly ( P<0.0001) lower (mean± SD, 6.1±1.3 m/s) than carotid-femoral PWV provided by arterial tonometry (mean± SD , 8.8±3.1 m/s). The average of differences between PWV values provided by the 2 methods (±1.96×SD) was -2.7±5.7 m/s. Conclusions The Mobil-O-Graph provides PWV values related to an ideal subject for a given age and blood pressure, but it is not able to evaluate early vascular aging expressed by high PWV in the individual patient. This is well shown in patients with Marfan syndrome.

Mechanical characterisation of human ascending aorta dissection

Mechanical characteristics of both the healthy ascending aorta and acute type A aortic dissection were investigated using in vitro biaxial tensile tests, in vivo measurements via transoesophageal echocardiography and histological characterisations. This combination of analysis at tissular, structural and microstructural levels highlighted the following: (i) a linear mechanical response for the dissected intimomedial flap and, conversely, nonlinear behaviour for both healthy and dissected ascending aorta; all showed anisotropy; (ii) a stiffer mechanical response in the longitudinal than in the circumferential direction for the healthy ascending aorta, consistent with the histological quantification of collagen and elastin fibre density; (iii) a link between dissection and ascending aorta stiffening, as revealed by biaxial tensile tests. This result was corroborated by in vivo measurements with stiffness index, β, and Peterson modulus, E_p, higher for patients with dissection than for control patients. It was consistent with histological analysis on dissected samples showing elastin fibre dislocations, reduced elastin density and increased collagen density. To our knowledge, this is the first study to report biaxial tensile tests on the dissected intimomedial flap and in vivo stiffness measurements of acute type A dissection in humans.

Predissection-derived geometric and distensibility indices reveal increased peak longitudinal stress and stiffness in patients sustaining acute type A aortic dissection: Implications for predicting dissection

OBJECTIVE

To assess ascending aortic distensibility and build geometry and distensibility-based patient-specific stress distribution maps in patients sustaining type A aortic dissection (TAAD) using predissection noninvasive imaging.

METHODS

Review of charts from patients undergoing surgical repair of TAAD (n = 351) led to the selection of a subset population (n = 7) with 2 or more predissection computed tomography angiography scans and echocardiograms at least 1 year before dissection. Ascending aortic wall biomechanical properties (aortic strain, distensibility, and stiffness) were compared with age- and size-matched nondissected nonaneurysmal controls. Patient-specific aortic strain served as an input in aortic geometry-based simulated 3-dimensional reconstructions to generate longitudinal and circumferential wall stress maps. Inspection of perioperative dissection scans and intraoperative visual examination confirmed primary tear locations.

RESULTS

Predissection echocardiography revealed ascending aortas of patients sustaining TAAD to exhibit decreased aortic wall strain (14.50 ± 1.13% vs 8.49 ± 1.08%; P < .01), decreased distensibility (4.26 ± 0.44 vs 2.39 ± 0.33 10^-6 cm²·dyne^-1; P < .01), increased stiffness (3.84 ± 0.24 vs 7.48 ± 1.05; P < .001), and increased longitudinal wall stress (246 ± 22 vs 172 ± 37 kPa; P < .01). There was no significant difference in circumferential wall stress. Predissection computed tomography angiography models revealed overlap between regions of increased longitudinal wall stress and primary tear sites.

CONCLUSIONS

Using predissection imaging, we identified increased stiffness and longitudinal wall stress in ascending aortas of patients with dissection. Patient-specific imaging-derived biomechanical property maps like these may be instrumental toward designing better prediction models of aortic dissection potential.

Are aortic coarctation and rheumatoid arthritis different models of aortic stiffness? Data from an echocardiographic study

Background

Patients who underwent a successful repair of the aortic coarctation (CoA) show high risk for cardiovascular (CV) events. Mechanical and structural abnormalities in the ascending aorta (Ao) might have a role in the prognosis of CoA patients. We analyzed the elastic properties of Ao measured as aortic stiffness index (AoSI) in CoA patients in the long-term period and we compared AoSI with a cohort of 38 patients with rheumatoid arthritis (RA) and 38 non-RA matched controls.

Methods

Data from 19 CoA patients were analyzed 28 ± 13 years after surgery. Abnormally high AoSI was diagnosed if AoSI > 6.07% (95th percentile of the AoSI detected in our reference healthy population). AoSI was assessed at the level of the aortic root by two-dimensional guided M-mode evaluation.

Results

CoA patients showed more than two-fold higher AoSI compared to RA and controls (9.8 ± 12.6 vs 4.8 ± 2.5% and 3.1 ± 2.0%, respectively; all p < 0.05 and in 5 of 19 patients with CoA (26%) AoSI was exceptionally high. The 5 patients with abnormally high AoSI were older with higher BP, LV mass and prevalence of LV diastolic dysfunction. Multiple linear regression analysis revealed that AoSI was independently related to the presence of LV hypertrophy and higher LV relative wall thickness.

Conclusions

CoA patients have higher AoSI levels than RA patients and non-RA matched controls. AoSI levels are abnormally high in a small sub-group of CoA patients who show a very high-risk clinical profile for adverse CV events.

Aortic dilatation in Marfan syndrome: role of arterial stiffness and fibrillin-1 variants

OBJECTIVE

Marfan syndrome (MFS) is an autosomal dominant genetic disorder characterized by aortic root dilation and dissection and an abnormal fibrillin-1 synthesis. In this observational study, we evaluated aortic stiffness in MFS and its association with ascending aorta diameters and fibrillin-1 genotype.

METHODS

A total of 116 Marfan adult patients without history of cardiovascular surgery, and 144 age, sex, blood pressure and heart rate matched controls were enrolled. All patients underwent arterial stiffness evaluation through carotid-femoral pulse wave velocity (PWV) and central blood pressure waveform analysis (PulsePen tonometer). Fibrillin-1 mutations were classified based on the effect on the protein, into 'dominant negative' and 'haploinsufficient' mutations.

RESULTS

PWV and central pulse pressure were significantly higher in MFS patients than in controls [respectively 7.31 (6.81-7.44) vs. 6.69 (6.52-6.86) m/s, P = 0.0008; 41.3 (39.1-43.5) vs. 34.0 (32.7-35.3) mmHg, P < 0.0001], with a higher age-related increase of PWV in MFS (β 0.062 vs. 0.036). Pressure amplification was significantly reduced in MFS [18.2 (15.9-20.5) vs. 33.4 (31.6-35.2)%, P < 0.0001]. Central pressure profile was altered even in MFS patients without aortic dilatation. Multiple linear regression models showed that PWV independently predicted aortic diameters at the sinuses of Valsalva (ß = 0.243, P = 0.002) and at the sinotubular junction (ß = 0.186, P = 0.048). PWV was higher in 'dominant negative' than 'haploinsufficient' fibrillin-1 mutations [7.37 (7.04-7.70) vs. 6.60 (5.97-7.23) m/s, P = 0.035], although this difference was not significant after adjustment.

CONCLUSION

Aortic stiffness is increased in MFS, independently from fibrillin-1 genotype and is associated with diameters of ascending aorta. Alterations in central hemodynamics are present even when aortic diameter is within normal limits. Our findings suggest an accelerated arterial aging in MFS.

Disruption of mechanical stress in extracellular matrix is related to Stanford type A aortic dissection through down-regulation of Yes-associated protein

In this study, we assessed whether the down-regulation of Yes-associated protein (YAP) is involved in the pathogenesis of extracellular matrix (ECM) mechanical stress-induced Stanford type A aortic dissection (STAAD). Human aortic samples were obtained from heart transplantation donors as normal controls and from STAAD patients undergoing surgical replacement of the ascending aorta. Decreased maximum aortic wall velocity, ECM disorders, increased VSMC apoptosis, and YAP down-regulation were identified in STAAD samples. In a mouse model of STAAD, YAP was down-regulated over time during the development of ECM damage, and increased VSMC apoptosis was also observed. YAP knockdown induced VSMC apoptosis under static conditions in vitro, and the change in mechanical stress induced YAP down-regulation and VSMC apoptosis. This study provides evidence that YAP down-regulation caused by the disruption of mechanical stress is associated with the development of STAAD via the induction of apoptosis in aortic VSMCs. As STAAD is among the most elusive and life-threatening vascular diseases, better understanding of the molecular pathogenesis of STAAD is critical to improve clinical outcome.

Assessment of the structure and function of the aorta by echocardiography

Echocardiography is the primary modality for imaging the aorta for the diagnosis and serial evaluation of pathological conditions. In this article, we review the methodology for optimal echocardiographic imaging of the various segments of the aorta and discuss abnormalities of the aorta including stenosis, dilation including aortopathy and sinus of Valsalva aneurysms, and fistulous communications involving the ascending aorta including aortoventricular tunnel and ruptured sinus of Valsalva aneurysm. We review novel echocardiographic measurements of aortic functional properties of the aorta such as elasticity and stiffness, and review the literature on the potential additive value of such measurements for structural assessment alone. Finally, we discuss the limitations of echocardiography in the precise and optimal imaging of the aorta.

Noninvasive Imaging of Flow and Vascular Function in Disease of the Aorta

With advancements in technology and a better understanding of human cardiovascular physiology, research as well as clinical care can go beyond dimensional anatomy offered by traditional imaging and investigate aortic functional properties and the impact disease has on this function. Linking the knowledge of the histopathological changes with the alterations in aortic function observed on noninvasive imaging results in a better understanding of disease pathophysiology. Translating this to clinical medicine, these noninvasive imaging assessments of aortic function are proving to be able to diagnose disease, better predict risk, and assess response to therapies. This review is designed to summarize the various hemodynamic measures that can characterize the aorta, the various noninvasive techniques, and applications for various disease states.

Ambulatory (24 h) blood pressure and arterial stiffness measurement in Marfan syndrome patients: a case control feasibility and pilot study

BACKGROUND

The aim of this work is the investigation of measures of ambulatory brachial and aortic blood pressure and indices of arterial stiffness and aortic wave reflection in Marfan patients.

METHODS

A case-control study was conducted including patients with diagnosed Marfan syndrome following Ghent2 nosology and healthy controls matched for sex, age and daytime brachial systolic blood pressure. For each subject a 24 h ambulatory blood pressure and 24 h pulse wave analysis measurement was performed.

RESULTS

All parameters showed a circadian pattern whereby pressure dipping was more pronounced in Marfan patients. During daytime only Marfan patients with aortic root surgery showed increased pulse wave velocity. In contrast, various nighttime measurements, wave reflection determinants and circadian patterns showed a significant difference.

CONCLUSIONS

The findings of our study provide evidence that ambulatory measurement of arterial stiffness parameters is feasible and that these determinants are significantly different in Marfan syndrome patients compared to controls in particular at nighttime. Further investigation is therefore indicated.

Losartan Attenuates Degradation of Aorta and Lung Tissue Micromechanics in a Mouse Model of Severe Marfan Syndrome

Marfan syndrome (MFS) is an autosomal dominant disease of the connective tissue due to mutations in the fibrillin-1 gene (FBN1). This study aimed at characterizing microelastic properties of the ascending aortic wall and lung parenchyma tissues from wild type (WT) and age-matched Fbn1 hypomorphic mice (Fbn1(mgR/mgR) mice) to identify tissue-specific biomechanical effects of aging and disease in MFS. Atomic force microscopy was used to indent lung parenchyma and aortic wall tissues, using Hybrid Eshelby Decomposition analysis to extract layer-specific properties of the intima and media. The intima stiffened with age and was not different between WT and Fbn1(mgR/mgR) tissues, whereas the media layer of MFS aortas showed progressive structural and mechanical degradation with a modulus that was 50% softer than WT by 3.5 months of age. Similarly, MFS mice displayed progressive structural and mechanical deterioration of lung tissue, which was over 85% softer than WT by 3.5 months of age. Chronic treatment with the angiotensin type I receptor antagonist, losartan, attenuated the aorta and lung tissue degradation, resulting in structural and mechanical properties not significantly different from age-matched WT controls. By revealing micromechanical softening of elastin-rich aorta and lung tissues with disease progression in fibrillin-1 deficient mice, our findings support the use of losartan as a prophylactic treatment that may abrogate the life-threatening symptoms of MFS.

Cardiac remodeling in the mouse model of Marfan syndrome develops into two distinctive phenotypes

Marfan syndrome (MFS) is a systemic disorder of connective tissue caused by mutations in fibrillin-1. Cardiac dysfunction in MFS has not been characterized halting the development of therapies of cardiac complication in MFS. We aimed to study the age-dependent cardiac remodeling in the mouse model of MFS FbnC1039G+/- mouse [Marfan heterozygous (HT) mouse] and its association with valvular regurgitation. Marfan HT mice of 2-4 mo demonstrated a mild hypertrophic cardiac remodeling with predominant decline of diastolic function and increased transforming growth factor-β canonical (p-SMAD2/3) and noncanonical (p-ERK1/2 and p-p38 MAPK) signaling and upregulation of hypertrophic markers natriuretic peptides atrium natriuretic peptide and brain natriuretic peptide. Among older HT mice (6-14 mo), cardiac remodeling was associated with two distinct phenotypes, manifesting either dilated or constricted left ventricular chamber. Dilatation of left ventricular chamber was accompanied by biochemical evidence of greater mechanical stress, including elevated ERK1/2 and p38 MAPK phosphorylation and higher brain natriuretic peptide expression. The aortic valve regurgitation was registered in 20% of the constricted group and 60% of the dilated group, whereas mitral insufficiency was observed in 40% of the constricted group and 100% of the dilated group. Cardiac dysfunction was not associated with the increase of interstitial fibrosis and nonmyocyte proliferation. In the mouse model fibrillin-1, haploinsufficiency results in the early onset of nonfibrotic hypertrophic cardiac remodeling and dysfunction, independently from valvular abnormalities. MFS heart is vulnerable to stress-induced cardiac dilatation in the face of valvular regurgitation, and stress-activated MAPK signals represent a potential target for cardiac management in MFS.

Biomechanical properties of the Marfan's aortic root and ascending aorta before and after personalised external aortic root support surgery

Marfan syndrome is an inherited systemic connective tissue disease which may lead to aortic root disease causing dilatation, dissection and rupture of the aorta. The standard treatment is a major operation involving either an artificial valve and aorta or a complex valve repair. More recently, a personalised external aortic root support (PEARS) has been used to strengthen the aorta at an earlier stage of the disease avoiding risk of both rupture and major surgery. The aim of this study was to compare the stress and strain fields of the Marfan aortic root and ascending aorta before and after insertion of PEARS in order to understand its biomechanical implications. Finite element (FE) models were developed using patient-specific aortic geometries reconstructed from pre and post-PEARS magnetic resonance images in three Marfan patients. For the post-PEARS model, two scenarios were investigated-a bilayer model where PEARS and the aortic wall were treated as separate layers, and a single-layer model where PEARS was incorporated into the aortic wall. The wall and PEARS materials were assumed to be isotropic, incompressible and linearly elastic. A static load on the inner wall corresponding to the patients' pulse pressure was applied. Results from our FE models with patient-specific geometries show that peak aortic stresses and displacements before PEARS were located at the sinuses of Valsalva but following PEARS surgery, these peak values were shifted to the aortic arch, particularly at the interface between the supported and unsupported aorta. Further studies are required to assess the statistical significance of these findings and how PEARS compares with the standard treatment.

Distinct effects of losartan and atenolol on vascular stiffness in Marfan syndrome

We conducted a randomized, double-blind trial of losartan (100 mg QD) versus atenolol (50 mg QD) for 6 months in adults with Marfan syndrome. Carotid-femoral pulse wave velocity (PWV), central augmentation index (AIx), aortic diameter and left ventricular (LV) function were assessed with arterial tonometry and echocardiography. Thirty-four subjects (18 female; median age 35 years, IQR 27, 45) were randomized. Central systolic and diastolic blood pressure decreased comparably with atenolol and losartan (p = 0.64 and 0.31, respectively); heart rate decreased with atenolol (p = 0.02), but not with losartan. PWV decreased in patients treated with atenolol (-1.15 ± 1.68 m/s; p = 0.01), but not in those treated with losartan (-0.22 ± 0.59 m/s; p = 0.15; between-group difference p = 0.04). In contrast, AIx decreased in the losartan group (-9.6 ± 8.6%; p < 0.001) but not in the atenolol group (0.9 ± 6.2%, p = 0.57; between-group difference p < 0.001). There was no significant change in aortic diameters or LV ejection fraction in either treatment group. In adults with Marfan syndrome, 6 months of treatment with atenolol improves PWV, whereas losartan reduces the AIx. By improving vascular stiffness via distinct mechanisms of action, there is physiologic value to considering the use of both medications in individuals with Marfan syndrome.

Pulse wave velocity involving proximal portions of the aorta correlates with the degree of aortic dilatation at the sinuses of valsalva in ascending thoracic aortic aneurysms

OBJECTIVE

To determine the relationship between arterial stiffness measured in different aortic segments and the presence and extent of ascending thoracic aortic aneurysm (ATAA).

METHODS

Patients at a Thoracic Aortic Diseases clinic at a University teaching hospital were compared to patients attending a Cardiology outpatient Clinic at the same institution. A non-invasive measure of vascular stiffness was performed using pulse wave velocity (PWV) measurement of several vascular segments-carotid-femoral pulse wave velocity (cfPWV), heart-femoral pulse wave velocity (hfPWV) and brachial-ankle pulse wave velocity (baPWV). Aortic dimensions were measured on echocardiogram.

RESULTS

Patients with ATAA (N = 32) were 66 years and the same age as those without ATAA (N = 46). There was no significant difference between those with or without aortic aneurysm with respect to cfPWV, hfPWV or baPWV. In ATAA, there was a significant (p <0.05) inverse correlation between aortic diameter at the sinuses of Valsalva and cfPWV, as well as hfPWV, but not with baPWV. This relationship was not evident in persons without ATAA.

CONCLUSION

Reduced aortic stiffness (increased compliance), assessed by cfPWV or hfPWV, correlates with larger aortic size of ATAA at the level of the sinuses of Valsalva but not at the ascending aorta, suggesting cfPWV may be a useful method to assess the size of ATAA at the level of the sinuses of Valsalva. Overall aortic stiffness assessed by PWV did not differentiate persons with or without an ATAA, in individuals who do not have a genetic or inheritable cause of their ATAA.

Perioperative transesophageal echocardiography for aortic dissection

PURPOSE

Aortic dissection is an infrequent but serious condition that often requires immediate operative intervention. We explore recent developments in the classification of aortic dissection and perioperative transesophageal echocardiography that assist with quantifying the severity of disease and facilitate its management.

PRINCIPAL FINDINGS

We describe the pivotal role of echocardiography in relation to key surgical considerations such as cannulation, aortic root surgery, perfusion in the aortic arch vessels, stenting in hybrid arch repair, and timing of preventative surgery.

CONCLUSION

Developments in the classification of aortic dissection have improved our perspective and understanding of the key presenting features that affect mortality. Improvements in patient outcome may be achieved in part by appropriately timed echocardiography-guided surgery.

Multidisciplinary approach to a Marfan syndrome patient with emphasis on cardiovascular complications

BACKGROUND

Marfan syndrome (MFS) is the most common inherited disorder of connective tissue affecting multiple organ systems. The most life-threatening and life-shortening complication is aortic dissection. Without surgery, life expectancy of MFS patients is reduced to approximately 32 years. Early identification and appropriate multidisciplinary medical cooperation is essential.

CONCLUSION

Proper follow up, therapy and timely surgical repair lead to an almost normal lifespan in affected individuals.

Impaired vascular contractility and aortic wall degeneration in fibulin-4 deficient mice: effect of angiotensin II type 1 (AT1) receptor blockade

Medial degeneration is a key feature of aneurysm disease and aortic dissection. In a murine aneurysm model we investigated the structural and functional characteristics of aortic wall degeneration in adult fibulin-4 deficient mice and the potential therapeutic role of the angiotensin (Ang) II type 1 (AT₁) receptor antagonist losartan in preventing aortic media degeneration. Adult mice with 2-fold (heterozygous Fibulin-4^+/R) and 4-fold (homozygous Fibulin-4^R/R) reduced expression of fibulin-4 displayed the histological features of cystic media degeneration as found in patients with aneurysm or dissection, including elastin fiber fragmentation, loss of smooth muscle cells, and deposition of ground substance in the extracellular matrix of the aortic media. The aortic contractile capacity, determined by isometric force measurements, was diminished, and was associated with dysregulation of contractile genes as shown by aortic transcriptome analysis. These structural and functional alterations were accompanied by upregulation of TGF-β signaling in aortas from fibulin-4 deficient mice, as identified by genome-scaled network analysis as well as by immunohistochemical staining for phosphorylated Smad2, an intracellular mediator of TGF-β. Tissue levels of Ang II, a regulator of TGF-β signaling, were increased. Prenatal treatment with the AT₁ receptor antagonist losartan, which blunts TGF-β signaling, prevented elastic fiber fragmentation in the aortic media of newborn Fibulin-4^R/R mice. Postnatal losartan treatment reduced haemodynamic stress and improved lifespan of homozygous knockdown fibulin-4 animals, but did not affect aortic vessel wall structure. In conclusion, the AT₁ receptor blocker losartan can prevent aortic media degeneration in a non-Marfan syndrome aneurysm mouse model. In established aortic aneurysms, losartan does not affect aortic architecture, but does improve survival. These findings may extend the potential therapeutic application of inhibitors of the renin-angiotensin system to the preventive treatment of aneurysm disease.

Aortic stiffness: current understanding and future directions. J Am Coll Cardiol. 2011;57:1511-1522. [PMID: 21453829 DOI: 10.1016/j.jacc.2010.12.017]

The aorta stiffens with aging, a process that is accelerated by arterial hypertension. Decreased arterial compliance is one of the earliest detectable manifestations of adverse structural and functional changes within the vessel wall. The use of different imaging techniques optimized for assessment of vascular elasticity and quantification of luminal and vessel wall parameters allows for a comprehensive and detailed view of the vascular system. In addition, several studies have also documented the prognostic importance of arterial stiffness (AS) in various populations as an independent predictor of cardiovascular morbidity and all-cause mortality. Measurement of AS by applanation tonometry with pulse-wave velocity has been the gold-standard method and is well-validated in large populations as a strong predictor of adverse cardiovascular outcomes. Because aortic stiffness depends on the prevailing blood pressure, effective antihypertensive treatment is expected to reduce it in proportion to the blood pressure reduction. Nevertheless, drugs lowering blood pressure might differ in their effects on structure and function of the arterial walls. This review paper not only will discuss the current understanding and clinical significance of AS but also will review the effects of various pharmacological and nonpharmacological interventions that can be used to preserve the favorable profile of a more compliant and less stiff aorta.

Molecular simulations predict novel collagen conformations during cross-link loading

Collagen cross-linking mechanically strengthens tissues during development and aging, but there is limited data describing how force transmitted across cross-links affects molecular conformation. We used Steered Molecular Dynamics (SMD) to model perpendicular force through a side chain. Results predicted that collagen peptides have negligible bending resistance and that mechanical force causes helix disruption below covalent bond failure strength, suggesting alternative molecular conformations precede cross-link rupture and macroscopic damage during mechanical loading.

Fibrillin-1 genetic deficiency leads to pathological ageing of arteries in mice

Fibrillin-1, the major component of extracellular microfibrils that associate with insoluble elastin in elastic fibres, is mainly synthesized during development and postnatal growth and is believed to guide elastogenesis. Mutations in the fibrillin-1 gene cause Marfan syndrome, a multisystem disorder characterized by aortic aneurysms and dissections. The recent finding that early deficiency of elastin modifies vascular ageing has raised the possibility that fibrillin-1 deficiency could also contribute to late-onset pathology of vascular remodelling. To address this question, we examined cardiovascular function in 3-week-old, 6-month-old, and 24-month-old mice that are heterozygous for a hypomorphic structural mutation of fibrillin-1 (Fbn1{+/mgΔ} mice). Our results indicate that Fbn1{+/mgΔ} mice, particularly those that are 24 months old, are slightly more hypotensive than wild-type littermates. Additionally, aneurysm and aortic insufficiency were more frequently observed in ageing Fbn1{+/mgΔ}$ mice than in the wild-type counterparts. We also noted substantial fragmentation and decreased number of elastic lamellae in the aortic wall of Fbn1{+/mgΔ} mice, which were correlated with an increase in aortic stiffness, a decrease in vasoreactivity, altered expression of elastic fibre-related genes, including fibrillin-1 and elastin, and a decrease in the relative ratio between tissue elastin and collagen. Collectively, our findings suggest that the heterozygous mgΔ mutation accelerates some aspects of vascular ageing and eventually leads to aortic manifestations resembling those of Marfan syndrome. Importantly, our data also indicate that vascular abnormalities in Fbn1{+/mgΔ} mice are opposite to those induced by elastin haploinsufficiency during ageing that affect blood pressure, vascular dimensions, and number of elastic lamellae.

Role of echocardiography in the assessment and management of adult congenital heart disease in pregnancy

Congenital heart disease represent a large proportion of heart disease in pregnancy. With the exception of patients with Eisenmenger's syndrome, pulmonary vascular obstructive disease, and Marfan's syndrome with aortopathy, maternal death during pregnancy is rare in women with CHD but morbidity occurs such as heart failure, arrhythmias, and stroke. Echocardiography represents a milestone in diagnosis, understanding of pathophysiology, assessment of disease severity and patient monitoring in pregnant women with unoperated and post-operative congenital heart disease.

Arterial stiffness in the young: assessment, determinants, and implications

Arterial stiffness describes the rigidity of the arterial wall. Its significance owes to its relationship with the pulsatile afterload presented to the left ventricle and its implications on ventricular-arterial coupling. In adults, the contention that arterial stiffness as a marker and risk factor for cardiovascular morbidity and mortality is gaining support. Noninvasive methods have increasingly been adopted in both the research and clinical arena to determine local, segmental, and systemic arterial stiffness in the young. With adoption of these noninvasive techniques for use in children and adolescents, the phenomenon and significance of arterial stiffening in the young is beginning to be unveiled. The list of childhood factors and conditions found to be associated with arterial stiffening has expanded rapidly over the last decade; these include traditional cardiovascular risk factors, prenatal growth restriction, vasculitides, vasculopathies associated with various syndromes, congenital heart disease, and several systemic diseases. The findings of arterial stiffening have functional implications on energetic efficiency, structure, and function of the left ventricle. Early identification of arterial dysfunction in childhood may provide a window for early intervention, although longitudinal studies are required to determine whether improvement of arterial function in normal and at-risk paediatric populations will be translated into clinical benefits.

Dysfunction of endothelial and smooth muscle cells in small arteries of a mouse model of Marfan syndrome

BACKGROUND AND PURPOSE

Marfan syndrome, a connective tissue disorder caused by mutations in FBN1 encoding fibrillin-1, results in life-threatening complications in the aorta, but little is known about its effects in resistance vasculature.

EXPERIMENTAL APPROACH

Second-order mesenteric arteries from mice at 3, 6 and 10 months of age (n= 30) heterozygous for the Fbn1 allele encoding a cysteine substitution (Fbn1(C1039G/+)) were compared with those from age-matched control littermates.

KEY RESULTS

Stress-strain curves indicated that arterial stiffness was increased at 6 and 10 months of age in Marfan vessels. Isometric force measurement revealed that contraction in response to potassium (60 mM)-induced membrane depolarization was decreased by at least 28% in Marfan vessels at all ages, while phenylephrine (3 microM)-induced contraction was reduced by at least 40% from 6 months. Acetylcholine-induced relaxation in Marfan vessels was reduced to 70% and 45% of control values, respectively, at 6 and 10 months. Sensitivity to sodium nitroprusside was reduced at 6 months (pEC(50)= 5.64 +/- 0.11, control pEC(50)= 7.34 +/- 0.04) and 10 months (pEC(50)= 5.99 +/- 0.07, control pEC(50)= 6.99 +/- 0.14). Pretreatment with N(omega)-Nitro-L-arginine methyl ester (200 microM) had no effect on acetylcholine-induced relaxation in Marfan vessels, but reduced vasorelaxation in control vessels to 57% of control values. Addition of indomethacin (10 microM) and catalase (1000 U.mL(-1)) further inhibited vasorelaxation in Marfan vessels to a greater degree compared with control vessels.

CONCLUSIONS AND IMPLICATIONS

Pathogenesis of Marfan syndrome in resistance-sized arteries increases stiffness and impairs vasomotor function.

Augmentation index relates to progression of aortic disease in adults with Marfan syndrome

BACKGROUND

Noninvasive applanation tonometry (APT) is useful to assess aortic stiffness and pulse wave reflection. Moreover, APT can predict outcome in many conditions such as arterial hypertension. In this study, we test whether APT measurements relate to progression of aortic disease in Marfan syndrome (MFS).

METHODS

We performed APT in 50 consecutive, medically treated adults with MFS (19 men and 31 women aged 32 +/- 13 years), who had not undergone previous cardiovascular surgery. During 22 +/- 16 months of follow-up, 26 of these patients developed progression of aortic disease, which we defined as progression of aortic root diameters >or=5 mm/annum (18 individuals), aortic surgery >or=3 months after APT (seven individuals), or onset of acute aortic dissection any time after APT (one individual).

RESULTS

Univariate Cox regression analysis suggested an association of aortic disease progression with age (P = 0.001), total cholesterol levels (P = 0.04), aortic root diameter (P = 0.007), descending aorta diameter (P = 0.01), aortic root ratio (P = 0.02), and augmentation index (AIx@HR75; P < 0.006). Multivariate Cox regression analysis confirmed an independent impact on aortic disease progression exclusively for baseline aortic root diameters (hazard ratio = 1.347; 95% confidence interval (CI) 1.104-1.643; P = 0.003) and AIx@HR75 (hazard ratio = 1.246; 95% CI 1.029-1.508; P = 0.02). In addition, Kaplan-Meier survival curve analysis illustrated significantly lower rates of aortic root disease progression both with lower AIx@HR75 (P = 0.025) and with lower pulse wave velocity (PWV) values (P = 0.027).

CONCLUSIONS

We provide evidence that APT parameters relate to aortic disease progression in medically treated patients with MFS. We believe that APT has a potential to improve risk stratification in the clinical management of MFS patients.

Congenital aortic disease: 4D magnetic resonance segmentation and quantitative analysis

Automated and accurate segmentation of the aorta in 4D (3D+time) cardiovascular magnetic resonance (MR) image data is important for early detection of congenital aortic disease leading to aortic aneurysms and dissections. A computer-aided diagnosis (CAD) method is reported that allows one to objectively identify subjects with connective tissue disorders from 16-phase 4D aortic MR images. Starting with a step of multi-view image registration, our automated segmentation method combines level-set and optimal surface segmentation algorithms in a single optimization process so that the final aortic surfaces in all 16 cardiac phases are determined. The resulting aortic lumen surface is registered with an aortic model followed by calculation of modal indices of aortic shape and motion. The modal indices reflect the differences of any individual aortic shape and motion from an average aortic behavior. A Support Vector Machine (SVM) classifier is used for the discrimination between normal and connective tissue disorder subjects. 4D MR image data sets acquired from 104 normal volunteers and connective tissue disorder patients MR datasets were used for development and performance evaluation of our method. The automated 4D segmentation resulted in accurate aortic surfaces in all 16 cardiac phases, covering the aorta from the aortic annulus to the diaphragm, yielding subvoxel accuracy with signed surface positioning errors of -0.07+/-1.16 voxel (-0.10+/-2.05mm). The computer-aided diagnosis method distinguished between normal and connective tissue disorder subjects with a classification correctness of 90.4%.

Marfan syndrome-diagnosis and management

Marfan syndrome (MFS) is the most common inherited disorder of connective tissue that affects multiple organ systems. This autosomal-dominant condition has an incidence of 2-3 per 10,000 individuals. Although genetic testing is available, the diagnosis is still primarily made using the Ghent criteria. Early identification and appropriate management is critical for patients with MFS who are prone to the life-threatening cardiovascular complications of aortic dissection and rupture. Advances in the understanding of the cause of MFS, early recognition of the disorder, and subsequent institution of medical and surgical therapy has resulted in dramatic improvement in the prognosis of this patient population over the past few decades. Beta-blockers have been demonstrated to slow aortic growth and thus delay the time to aortic surgery. Operative intervention has markedly changed the prognosis of patients with MFS and can be safely performed on an elective basis. Identification of presymptomatic patients is critical to reduce the frequency of catastrophic aortic events.